The present invention relates to a shielded high-frequency apparatus having a partitioned shielding case, and a method of manufacturing such apparatus. More specifically, the present invention is directed towards a shielded high-frequency apparatus consisting of a partitioned shielding case having a printed circuit board mounted therein, with partitions of the case forming chambers for mutually isolating portions of the printed circuit board.
Such a shielded high-frequency apparatus is widely utilized at the present time to implement a high frequency receiver circuit operating in the UHF band, for use in a CATV system for example, in which the effects of radio wave interference must be suppressed.
FIG. 1 is an oblique view of a prior art shielded high-frequency apparatus of this type, which consists of a partitioned shielding case 1 and a printed circuit board 4, with the diagram showing the condition prior to inserting the printed circuit board 4 into the partitioned shielding case 1 to be attached therein as described hereinafter. FIG. 2 shows a junction between one of a set of three partition plates 3a, 3b and 3c and a frame 2 of the partitioned shielding case 1, whereby the partition plate is attached to the inner face of the frame 2 while in addition electrical shielding is established at the junction, while FIG. 3 shows a junction between the printed circuit board 4, a separate metal attachment member 6 which serves to attach the printed circuit board 4 to the frame 2, and the inner face of the frame 2. A plurality of such separate metal attachment members may be utilized.
The frame 2 is formed from metal plate in a rectangular shape as shown. The term "metal plate" as used in the present specification and claims signifies metal in thin, flat form, and is intended to apply to material such as sheet metal. The partition plates 3a, 3b and 3c are also formed from metal plate, and serve to partition the interior of the frame 2 as a shielding function. The printed circuit board 4 has electrical components 12 mounted thereon.
As shown in FIG. 2, a material 5 is disposed to provide a shield at each of the junctions between the partition plates 3a, 3b and 3c and the frame 2, and also to mutually attach the partition plates 3a, 3b and 3c and the frame 2. Such material is also disposed for shielding the junctions at which the partition plates 3a, 3b and 3c mutually intersect as shown in FIG. 1, and to mutually attach the partition plates 3a, 3b and 3c.
The separate metal attachment member 6 is provided with lugs 6' which are utilized for solder attachment of the separate metal attachment member 6 to both the partitioned shielding case 1 and to a portion of a printed circuit pattern on the printed circuit board 4 that is to be at ground potential, to thereby attach the printed circuit board 4 to the partitioned shielding case 1 and also establish electrical ground connection between these.
This prior art apparatus is assembled as follows. First, the two laterally extending partition plates 3a and 3b and the vertically extending partition plate 3c (as viewed in plan) are inserted in the frame 2, and the junction portions between these partition plates 3a, 3b and 3c and the inner face of the frame 2, and between the intersections of the partition plates 3a, 3b and 3c, are mutually attached by the shielding material 5. The shielding material 5 generally consists of copper foil, which is brazed in order to establish the aforesaid attachment. However in some cases solder may be used. Irrespective of the type of shielding material which is used, manual operations must be executed in order to establish the mutual attachments described above.
The printed circuit board 4 is then inserted into the frame 2, and then is attached to the partitioned shielding case 1 and also electrically connected to the partitioned shielding case 1 (i.e. connection between a ground lead pattern of the printed circuit board 4 and the partitioned shielding case 1) by soldering the lugs 6' of the separate metal attachment member 6 as shown in FIG. 3. This soldering operation is performed manually, using solder 7 which has been deposited on the lugs 6'.
Such a prior art shielded high-frequency apparatus presents the following problems. First, if copper foil is used as the shield material 5, then high-temperature copper brazing must be carried out. This can result in warping of the partitioned shielding case 1. In addition, plating processing may be necessary after completion of such copper brazing, so that the manufacturing cost of such a shielded high-frequency apparatus will be high and the dimensional accuracy will be poor.
If on the other hand solder is used as the shield material 5, then it is necessary to perform deposition of solder on the frame 2 beforehand, by solder plating. This may result in excess amounts of solder being left deposited on the frame 2, or extraneous fringes or spikes of excess solder may be formed, making it necessary to remove the excess solder, e.g. by a process such as immersing the frame 2 in oil. In addition to the above problems, such a method results in large quantities of solder being utilized in the manufacturing process.
Furthermore when the printed circuit board 4 and the partitioned shielding case 1 are mutually attached by soldering using the separate metal attachment member 6, there is a danger that "dry joints" may be produced in the solder connections, so that lower reliability may occur. Moreover when the printed circuit board 4 and the partitioned shielding case 1 are mutually attached by such a separate metal attachment member 6 having solder lugs 6' as in this example, it will in fact be necessary to use a plurality of such separate attachment members.